Renal plasma flow and glomerular filtration rate were estimated simultaneously in the conscious rat by the "average total body clearance" of tetraethyl-ammonium (TEA) and inulin, calculated as Dose i.v./AUC, in which AUC represents the area under the plasma disappearance curve of 14C or 3H plasma radioactivity after a single injection into the tail vein of a solution containing both 14C-TEA and 3H-methoxyinulin.